This invention relates to an improved device for locking reciprocating piston type fluid actuators in a desired position. A particular application for such improved actuator locking device is the piston actuator connected to the rams of a ram type oilfield blowout preventer.
When oilfield ram type blowout preventers are in use, it occasionally becomes necessary to lock the rams in the closed position. The prior art of blowout preventers has numerous devices for locking a ram in its closed position. Such devices range from a simple mechanical screw which is threaded through the bonnet to engage the outer end of the ram connecting rod or piston to prevent its movement in the outward direction to complicated devices such as shown in U.S. Pat. No. 4,305,565 wherein a locking cone responds to fluid pressure during the movement of the ram to move the locking wedges into engagement with the tapered inner surfaces of the housing.
Another ram lock structure is shown in U.S. Pat. No. 3,941,141 which includes slip-like structures operated on a dovetail for movement of the slips to engage the threads on the tail rod.
Other prior art patents, such as U.S. Pat. Nos. 4,052,995 and 4,076,208 and 4,290,577 disclose ram locks wherein a lock nut is stopped from rotating by a clutch mechanism which has ratchet teeth.
U.S. Pat. No. 2,845,902 discloses a self-locking fluid linear actuator which utilizes cones in a tapered section for locking following movement but is released responsive to hydraulic pressure.